I experienced something similar developing http://FightTheFloods.com - the site was conceived and launched in a 24 hr period. I didn't have collaboration concerns though, it was me coding and my girlfriend doing design so we didn't have to worry about merging etc too much.

I think that perhaps the best thing to do is to have frameworks in place ready to manage these types of events. They'd follow a similar formula (after FightTheFloods was launched 3 or more similar websites started up, so there's a clear design pattern here) and could be customized to suit each event rather quickly. That way the interaction design can be thought out prior to the quick rush of getting the site up and in use.

A moving commentary narrating noble efforts.

I'm positive the community brainstorming subsequent to this could be of great use whenever such unfortunate (and unavoidable) events take place in times to come.